MOSCOW — Russia chided its longtime ally Syria on Tuesday over its threat to use chemical weapons in case of a foreign attack, but Moscow gave no sign it was abandoning President Bashar Assad’s regime, despite growing international condemnation over the violence in the Arab country.

Syria is Russia’s last remaining ally in the Middle East and hosts the only naval base Moscow has outside the former Soviet Union. Russia has protected Syria from international sanctions and supplied it with weapons amid an escalating civil war.

On Monday, Syria threatened to unleash its chemical and biological weapons if it faces a foreign attack — its first-ever acknowledgement it possesses weapons of mass destruction.

In a statement that reflected a degree of irritation with Assad, the Russian Foreign Ministry reminded Syria that it had ratified a global convention banning the use of chemical weapons. It added that Russia expects Syria to “unfailingly honor its international obligations.”

The statement follows earlier Russian rebukes of Assad’s heavy-handed use of force and slow pace of reforms.

But despite occasional criticism, Russia has staunchly refused to back international calls for the Syrian strongman to step down, saying that foreign players have no right to determine the nation’s political future, and that it must be decided by Syrians themselves.

Syria’s Ambassador to Cyprus Lamia al-Hariri resigned her post on Tuesday and reportedly fled to Qatar. Al-Hariri became the third Syrian diplomat to defect, following the ambassador to Sweden, Bassam Imadi, in December, and Nawaf Fares, the ambassador to Iraq, in July.

A 16-month uprising in Syria has morphed into a civil war has killed more than 19,000, according to the Britain-based Syrian Observatory for Human Rights. The escalating fighting is also feeding fears that Syria’s war could spill across borders and spark a regional conflagration.

Russian President Vladimir Putin made it clear Monday that Moscow would not join those pressuring Assad to step down. “If the Syrian leadership is ousted from power by unconstitutional means, the leadership and the opposition will trade places and the civil war will continue,” Putin said.

On Thursday, Russia and China vetoed a Western-backed United Nations resolution threatening Assad’s regime with sanctions — the third such double veto of a U.N. motion addressing the crisis. The next day, the U.N. Security Council unanimously approved a resolution Friday renewing the 300-strong U.N. observer force in Syria for another 30 days.